The present invention relates generally to antenna isolation circuits for transmitters and receivers using the same antenna. More specifically, but without limitation thereto, the present invention relates to an input/output isolation circuit that extracts energy from a radio frequency (RF) output signal to cancel undesired coupling of the RF output signal into one or more RF input devices.
It is often advantageous to couple multiple devices, such as a transmitter and a receiver, to the same antenna. A common approach uses a radio frequency circulator to isolate the transmitted signal from the received signal to avoid overloading the receiver front end. However, current technology for RF circulators limits the degree of isolation to about 25 dB. The conventional methods are therefore not suited to applications that require 50 dB or more of isolation. A need therefore exists for an antenna isolation circuit that attenuates the coupling of undesired RF signals by at least 50 dB.